1. Field of Invention
The present invention relates to power conversion, and more particularly, to reducing soft start delay and providing soft recovery in power system controllers.
2. Description of Related Art
Power converters are essential for many modern electronic devices. Among other capabilities, a power converter can adjust voltage level downward (buck converter and its derivatives) or adjust voltage level upward (boost converter and its derivatives). A power converter may also convert from alternating current (AC) power to direct current (DC) power, or vice versa. A power converter may also function to provide an output at a regulated level (e.g., 5.0V). Power converters are typically implemented using one or more switching devices, such as transistors, which are turned on and off to deliver power to the output of the converter. Control circuitry is provided to regulate the turning on and off of the switching devices, and thus, these converters are known as “switching regulators” or “switching converters.” Such a power converter may be incorporated into or used to implement a power supply—i.e., a switching mode power supply (SMPS). The power converters may also include one or more capacitors or inductors for alternately storing and outputting energy.
Some power converters may employ a soft-start circuit in order to begin operation after power on. The soft-start circuit may have a soft-start capacitor which must be charged to a predetermined voltage before the power converter delivers any power to a load. If the charging of the soft-start capacitor is slow, then power delivery is delayed.
Also, some power converters may employ a closed-loop feedback with an error amplifier to regulate output voltage. The closed loop operation maintains the error amplifier of the power converter in its linear operating mode to actively control the output voltage of the power converter to follow a reference voltage VREF at the non-inverting input of the error amplifier. A short circuit or brown-out condition may cause a significant drop in the value of the output voltage. If the error amplifier reference voltage VREF is independent from the feedback voltage, recovery after a short circuit or brown-out condition is usually followed by significant overshoot in the output voltage since the error amplifier is railed during these events and need to recover. Such overshoot in the output voltage is an undesired phenomenon in power supplies.